YOU SAID:
I broke my arm while on the subway yesterday
INTO JAPANESE
私は昨日地下鉄で腕を折った
BACK INTO ENGLISH
I broke my arm with the subway yesterday.
INTO JAPANESE
私は昨日地下鉄で腕を壊した。
BACK INTO ENGLISH
I broke my arm with the subway yesterday.
That didn't even make that much sense in English.